Along with the increasing degree of integration in recent years, patterns are becoming ever finer in fields such as the production of semiconductor circuits and lithography masks. As a result, resist materials of still higher resolution levels are required, and it has become necessary to be able to carry out the processing of <0.25 μm sub-quarter micron patterns at high sensitivity. Carrying out such minute processing by conventional lithography using a comparatively long wavelength light source is difficult, and lithography employing higher energy X-rays, electron beams and vacuum ultraviolet is being investigated, and resists corresponding to these radiation sources are being demanded.
As known resist materials having the characteristics of high sensitivity and high resolution corresponding to such sources of radiation exposure, chemically amplified resists have been extensively investigated. Chemically amplified resists are resists which possess a mechanism whereby acid is generated in exposed regions due to the action of a photoacid generator, and the solubility of the exposed regions is modified by the catalytic action of this acid. Hitherto, amongst such chemically-amplified resists those showing comparatively good resist properties have employed alkali-soluble resins in which the alkali-soluble groups are protected by acid labile groups such as the tert-butyl group, the 1,1-diphenylethyl group (U.S. Pat. No. 5,688,628), the trityl group (JP-A-6-83057) and other such tertiary ester groups, the tert-butoxycarbonyl group, the acetal group and the like.
However, there is an opposing relation between resolution and sensitivity, and there have been problems such as inadequate sensitivity when obtaining a resolution sufficient for carrying out sub-quarter micron pattern processing.